Station identification circuit arrangement

ABSTRACT

A universal station identification circuit arrangement for use with central office equipment that utilizes either differential or longitudinal detection methods is adapted to be connected to the tip party&#39;s subscribers drop in a two-party line without requiring access to or rewiring of the tip party&#39;s telephone. The circuit arrangement may be fabricated in a single unit which includes a ringer isolator and ANI mark circuits. The ringer isolator and the ANI mark circuits may also be used individually.

This application is a division of application Ser. No. 143,137, filedApr. 23, 1980.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to telephone system equipment that is used at thesubscriber's end of a subscriber's line in conjunction with a telephonestation, and in particular to a universal station identification circuitarrangement including a ringer isolator and ANI (Automatic NumberIdentification) mark circuits which are detected by central officeequipment utilizing either differential or longitudinal detectionmethods.

2. Discussion of the Relevant Art

Ringer isolator circuits are used to eliminate electrical noise thatresults from ringer ground connections during the talking state of atelephone call while the called and the calling parties are connected toeach other. This is accomplished by keeping the telephone ringerisolated or disconnected from ground except for the periods when acentral office ringing signal voltage is applied to ring the telephone.

ANI mark circuits (also referred to as station identification circuits)are used with plural party lines to identify toll calls dialed by aselected party (customarily the tip party as distinguished from the ringparty) for billing purposes in an automatic number identificationsystem.

Prior to this invention, it has generally been the practice to wireringer isolator and ANI mark circuits directly into the telephone sets.It also has been a custom to incorporate the ANI mark circuits into thetelephone sets at the time of manufacture, but to make the circuitconnections in such a way that the ANI mark circuits remain inactive ordisabled until such time that it is desired to install the telephone ata tip party station on a two-party line.

Because of this custom, service calls are frequently needed when atelephone set is later assigned to a new or different subscriber for thepurpose of converting the set in some cases to single party or ringparty use and in other cases to tip party use. Many times existingtelephones already installed are not equipped with ANI mark circuits. Ifconversion is required for tip party use, a service call is required,and physical access to the telephone is needed in order to make amodification to utilize a circuit arrangement which must be installed inthe instrument itself. In addition, house calls are required to equipsubscriber's telephones with the type of ringer isolator that isinstalled in the telephone itself.

In order to avoid the requirement of obtaining access to the physicaltelephone instrument, many circuits have been devised to provide the ANImark equipment in such a way that it need not be physically housed inthe instrument itself. One example of such an ANI mark circuit is shownin FIG. 2 of U.S. Pat. No. 4,001,512 issued to D. F. Proctor on Jan. 4,1977. Another example of this type of circuit is disclosed in U.S. Pat.No. 4,054,942 issued to C. W. Chambers, Jr., on Oct. 18, 1977.

Both of these ANI mark circuits may be installed without requiringaccess to the subscriber's telephone. As a result no changes arerequired in the telephone itself or in the wiring to the telephone todivert the telephone station to tip party use on a two-party line. TheANI mark circuits described in the above-mentioned patents, however,have serious drawbacks.

In both patents, for example, the circuits designs are such thatinsertion or line losses are created by electrical components which areconnected in the subscriber loop itself in series with one or both ofthe different ring conductors. In patent No. 4,054,942 and in one of theembodiments of patent No. 4,001,512 there is the additional problem ofelectrical noise which is created by grounding one of the two subscriberline conductors (usually the tip conductor) through a resistor, but notthe other conductor in the course of establishing the ground mark.

In another type of prior ANI mark circuit, the base-emitter junction ofa bipolar transistor is connected across a resistor that is in serieswith the tip conductor of the tip party's drop, and the collector of thetransistor is connected to ground through a resistor (usually 2.6Kohms). With this circuit design, loop current flow in the tip party'sloop circuit turns on the transistor to create a difference in thecurrent flowing in the tip and ring conductors. The resulting currentdifference is sensed by ANI equipment in the central office. This ANIstation identification circuit is referred to as the differential typeand cannot be employed with the longitudinal type of identification inwhich a current path to ground is sensed at the central office toidentify the calling party as the tip party.

Examples of prior ringer isolator circuits are described in U.S. Pat.No. 3,916,111 issued to H. W. Ott on Oct. 28, 1975, U.S. Pat. No.3,303,289 issued to M. S. Hawley, et al on Feb. 7, 1967 and U.S. Pat.No. 3,230,316 issued to P. M. Hunt on Jan. 18, 1966.

These patented ringer isolator circuits for the most part are normallywired into the telephone set itself and therefore present a problem ofobtaining access to the telephone to make the installation as mentionedearlier.

The present invention avoids the foregoing problems and drawbacks aswell as offering additional advantages as will become apparent from thefollowing summary and description.

SUMMARY OF THE INVENTION

The present invention provides a novel ringer isolator circuit capableof operating with reduced ringer voltages and a novel ANI mark orstation identification circuit which may be used individually orcombined into a common unit for connection to a subscriber's dropwithout requiring access to or rewiring of the subscriber's telephone.The unit containing the combined, electrically compatible ringerisolator and ANI mark circuits may also optionally include a stationprotector such as a gas tube arrestor. The present circuit arrangementis capable of being used with central office equipment that uses eitherdifferential or longitudinal detection methods for sensing theapplication of the mark signal which is sensed at the central office toidentify the calling party as the tip party. The ANI mark circuit ofthis invention operates to apply a ground mark in response to any (each)interruption of loop current after the tip party's telephone is liftedoff-hook to enable the central office equipment to sense the presence ofa current path to ground and is compatible with central office equipmentwhich utilizes either a differential or a longitudinal detection method.

When the differential detection method is used the ANI mark circuitarrangement provides a ground mark circuit responsive to the initialloop current flow when the tip party's telephone is lifted off-hook andenables a ground mark switching circuit to apply a tip-to-ground andring-to-ground mark. The application of a balanced tip-to-ground markand ring-to-ground mark through equal resistances is sensed by centraloffice equipment utilizing a differential detection method. When acentral office utilizes a longitudinal detection method generally -48volts is either placed on the tip or tip and ring shorted together andthe present circuit arrangement senses the loss of loop current andplaces a tip-to-ground mark completing a current path to ground wnhichis sensed by a central office utilizing a longitudinal detection method.

The ANI mark circuit of this invention is designed in such a way thatpractically no insertion or line losses or imbalances are introducedinto the tip party's line. Furthermore, the ANI mark circuit of thisinvention operates to remove the differential ground mark during openloop dialing pulses to avoid distortion of the pulses.

With the foregoing in mind, a major object of this invention is toprovide a novel ANI mark circuit which is not subject to the previouslydescribed disadvantages of prior ANI mark circuits and may be utilizedwith central office equipment utilizing either differential orlongitudinal detection methods.

The ringer isolator circuit of this invention is an electronic switchhaving a pair of capacitors connected in a voltage doubler circuit whichpermits it to operate at reduced ringer voltages. The telephone ringeris connected to ground only upon sensing the presence of ringing voltageacross the tip and ring sides of a telephone line. In the ringerisolator of this invention the central office ringing signal isrectified and voltage doubled via two diodes and two capacitors. Thesecond capacitor is connected across a neon tube. When the voltageacross the capacitor rises to preselected value, the neon tube is firedto emit light onto a light sensitive resistor. The light sensitiveresistor thereupon feeds gate current to a Triac to turn the Triac on.The Triac is connected between the telephone ringer and ground so thatwhen it turns on, it connects the ringer to ground.

One of the diodes utilized in the voltage doubling circuit is a zenerdiode that in addition to rectifying the incoming ringing signal, itprotects the capacitor against fault voltages.

By AC coupling incoming ringing signals into the voltage doublingcircuit of the ringer isolator, it is made non-polar (not polaritysensitive) and therefore cannot be used with superimposed four partyringing.

Another object of this invention is to provide a novel unit whichincorporates a combined ringer isolator and an ANI mark circuit that isadapted to be connected outdoors to a subscriber drop without requiringaccess to or rewiring of the subscriber's telephone.

A further object of this invention is to provide a novel ANI markcircuit which applies a ground mark in response to the interruption ofloop current after the tip party's telephone has been lifted offhook andalso provides a mark in response to loop current flow when a party islifted off-hook and which is utilizable with central office equipmentthat uses either differential or longitudinal detection methods.

Yet another object of this invention is to provide a novel ANI markcircuit which removes the differential ground mark during open loopdialing impulses to avoid distortion of the pulses.

A universal station identification circuit arrangement for use withcentral office equipment utilizing either differential or longitudinaldetection methods for identifying a preselected one of two parties on atwo-party line in a telephone system when a call is initiated from thepreselected party's telephone, comprising first means for providing afirst ground mark which is normally disconnected from the line when thepreselected party's telephone is on-hook; second means responsive to thenormal flow of loop current that is established by lifting thepreselected party's telephone off-hook for causing the first means toapply the first ground mark to both the tip and ring conductors of theline; third means for providing a second ground mark which is normallydisconnected from the line when the preselected party's telephone is onhook; and fourth means responsive to any momentary interruption of loopcurrent that occurs after the flow of loop current is established bylifting the preselected party's telephone off hook for causing the thirdmeans to apply a second mark to the tip conductor of the line.

The foregoing and other objects and advantages will appear from thedescription to follow. In the description reference is made to theaccompanying drawing which forms a part hereof, and in which is shown byway of illustration a specific embodiment in which the invention may bepracticed. This embodiment will be described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that structuralchanges may be made without departing from the scope of the invention.The following detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is best definedby the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a two-party telephone systemincorporating the principles of the present invention; and

FIG. 2 is a schematic circuit diagram of the ringer isolator and theuniversal station identification circuit arrangement (ANI mark circuit)of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the figures, and in particular to FIG. 1 where atwo-party subscriber loop circuit incorporating the principles of thepresent invention is shown comprising a tip party telephone station 12and the ring party telephone station 14.

The telephone set 16 and the tip party station 12 is connected by way ofa subscriber's drop 18 (sometimes referred to as a drop wire) and atelephone or transmission line 20 to a central office 22. The telephoneset 24 in the ring party station 14 is connected by a separatesubscriber's drop 26 and line 20 to the central office 22.

The line 20 is common to telephone stations 12 and 14 and has tip andring conductors 28 and 30 as shown. Drop 18 and line 20 combine todefine a first subscriber's loop or line for the tip party; and drop 26and line 20 combine to define a second subscriber's loop or line for thering party.

Still referring to FIG. 1, the subscriber drop 18 has tip and ringconductors 32 and 34, respectively, which connect to the tip and ringconductors 28 and 30, respectively, on line 20. Likewise, drop 26 hastip and ring conductors 36 and 38, respectively, which connect to thetip and ring conductors 28 and 30 of line 20.

Telephone set 16 comprises a conventional three wire circuit havingthree terminals 40, 41, and 42 for making wiring connections to theplant or facility outside of the subscriber's dwelling. As shown, set 16includes a ringer 44 and a capacitor 46 connected in series betweenterminals 40 and 41 and also a hook switch 48 and the handset 50connected in series between terminals 40 and 42.

The ring party's telephone set 24 is the same as the tip party'stelephone set 16. Like reference characters have therefore been appliedto designate corresponding components of sets 16 and 24 except that thereference numerals for set 24 have been suffixed by the letter "a" todistinguish them from the reference numerals applied to set 16.

The tip and ring party's station units incorporating the principles ofthe present invention are respectively indicated at 52 and 53 in FIG. 1.The tip party unit 52 is connected to the subscriber's end of drop 18,and the ring party unit 53 is similarly connected to the subscriber'send of drop 26. In the preferred embodiment unit 52 comprises a ringerisolator 54 and an ANI group mark station identification circuitarrangement 56. A station protector 58 may optionally be included inunit 52 as shown. The station protector 58 may be a conventional threeelectrode gas tube surge arrestor such as the series TII-300manufactured by the TII Corporation, Lindenhurst, N.Y.

Unit 52 is normally located outside of the tip party's home or buildingwhich houses telephone set 16 and which is schematically indicated indashed lines at 60 in FIG. 1. Terminals 40 through 42 of telephone set16 are connected by a three conductor station wire 62 to unit 52 in amanner to be described hereinafter.

As shown, the three conductors of the station wire 62 are indicated at64, 65, and 66 in FIG. 1 and are respectively connected to terminals 40,41 and 42. In this embodiment, the ringer isolator is provided with fouroperating terminals 68, 69, 70 and 71, and the ANI mark circuit 56 alsohas four terminals as indicated at 72, 73, 74, and 75.

As shown, the ring side or ring conductor 34 of drop 18 is connected toone end electrode of the gas tube surge protector 58, to terminals 68and 72 and through conductor 66 to terminal 42. The tip side or tipconductor 32 of drop 18 is connected to the upper end electrode ofprotector 58, and to terminals 69 and 74.

In the ANI mark circuit 56 a series current conducting path isestablished between terminals 74 and 75 through a relay 155 and aresistor 157 connected in series. A zener diode 158 is connected inparallel with the relay 155 and an oppositly poled diode 159 isconnected in parallel with resistor 157. A capacitor 156 is connected inparallel with the series connection of relay 155 and resistor 157 thusproviding an AC and DC path to extend the tip side of the line.Conductor 64 conneccts terminals 75 to terminal 40 and conductor 65connects terminal 41 to terminal 70. The center electrode of protector58 and terminals 71 and 73 are all connected by a common ground wire 82to earth ground.

With the circuit connections just described for the gas tube protector58, the gas tube will fire when lightening or other induced surge occursto cause both the tip and ring sides of drop 18 to become groundedthrough the gas tubes high conductivity ion path to the tubes centerelectrode which is connected to earth ground. The gas tube protector 58may also be of a two element construction well known in the art.

In addition to being electrically combined or connected in unit 52 inthe manner shown, protector 58, ring isolator 54 and the ANI markcircuit 56 may advantageously be incorporated into a common package orcontainer which is schematically indicated at 84 in FIG. 1.

Alternatively, protector 58 may be located outside of unit 52 andcontainer 84. With such an arrangement unit 52 will consist of ringerisolator 54 and the ANI mark circuit 56 and may be mounted at protector58. In either case, unit 52, with or without protector 58, makes accessto or rewiring of the station telephone 16 unnecessary.

Moreover, the ringer isolator 54 and the ANI mark circuit 56 may be usedindividually as separate components. As is apparent, access to orrewiring of the subscriber's telephone is also unnecessary when eitherthe ringer isolator 54 or the ANI mark circuit 56 is used individually.

The ring party unit 53 is the same as the tip party unit 52 except thatit does not have an ANI ground mark station identification circuit.Additionally, the circuit connections to the telephone set 24 and theringer isolator in unit 53 differ as will be described in detail lateron. To the extent that unit 53 is the same as unit 52, like referencenumerals suffixed by the letter "a" have been applied to designatecorresponding components of unit 53.

Referring now to FIG. 2, ringer isolator 54 constitutes an electronicswitch which senses the presence of ringing voltage and electricallyconnects the telephone ringer 44 to ground. To accomplish this, theillustrated embodiment of ringer isolator 54 is shown to comprise a pairof circuit arrangements 90 and 91 which are electrically isolated fromeach other in the sense that there is no metallic current conductingpair between them.

Circuit arrangement 90 includes a capacitor 92 connected in series witha diode 93 and a resistor 94 across terminals 69 and 68 of ringerisolator 54. A second series path between terminals 69 and 68 includescapacitor 92, zener diode 95, resistor 96 and capacitor 97. The cathodeelectrode of zener diode 95 and the anode electrode of diode 93 are bothconnected to capacitor 92. A resistor 98 and a two-terminal neon tube orbulb 99 are serially connected across capacitor 97. The circuitarrangement as described functions as a voltage doubler circuit so thatvoltage appearing across capacitor 97 will be approximately equal to thepeak to peak AC voltage appearing across terminals 69 and 68 since diode93 will conduct on one half of the AC cycle and diode 95 will conduct onthe other half of the AC cycle. Circuit arrangement 91 includes a Triac100 connected across terminals 70 and 71 of the ringer isolator 54. Azener diode 101 and a capacitor 102 connected in parallel as shown maybe connected in series with the Triac 100 as will be explainedhereinafter. A light-sensitive resistor 103 which is light coupled totube 99 functions to control the gate current to Triac 103.

As shown, resistor 103 is connected in series with a resistor 104 offixed resistance across the anode terminals of the Triac 100 with thegate electrode 105 of Triac 100 being connected to the juncture ofresistors 103 and 104. When no light is directed on resistor 103 itsresistance will be very high and effectively presents an open circuit.When light eminating from tube 99 impinges upon resistor 103 it becomesa relatively low resistance thereby supplying sufficient current intothe gate electrode of Triac 100 turning it on (putting it in itsconducting state).

From the description thus far it is clear that Triac 100 is connected inseries with ringer 44, capacitor 46 and ground. When Triac 100 is in itsnon-conducting state and no light is directed onto resistor 103, thecircuit between ringer 44 and ground will be open so that no current canbe conducted through the ringer. When Triac 100 is turned on, itcompletes the circuit for ringing ringer 44 so that current (AC) will beconducted from ground to conductor 82 to Triac 100 conductor 65, ringer44, capacitor 46, conductor 64, capacitor 156, and the tip side of drop18 to tip conductor 28.

In unit 52 which includes the circuit arrangements of 54 and 56,terminal 68 is connected to ring conductor 34 and hence the ring side ofline 20, while terminal 69 is connected to tip conductor 32 and hencetip of side of line 20 as previously spliced.

When it is desired to ring the tip party's telephone set 16, centraloffice equipment grounds the ring conductor of line 20, applies a DCcentral office battery potential to the tip conductor of line 20 andapplies an AC ringing signal voltage on the negative central officebattery potential at the tip side of line 20. This is typicallyaccomplished by connecting the central office ring generator (not shown)in series with the central office battery between the negative side ofthe battery and the tip conductor of line 20 at the central office. Theringing signal typically has a frequency of 20 Hz and a peak voltage of140 volts (80 to 100 volts RMS).

For the above example of central battery voltage, the DC voltage appliedacross terminal 68 and 69 will therefore be minus 48 volts, tip-to-ring,with minus 48 volts on terminal 69 and 0 volts on terminal 68. Zenerdiode 95 will therefore be forward biased under negative goingalternations of the ringing signal voltage and diode 93 will becomeforward biased on the positive alternations of the ringing signalvoltage. Zener diode 95 will become reversed biased and non-conductingwhen the positive going alternation of the ringing signal voltagebecomes positive. The zener potential of diodes 95 is selected to behigh enough such that the positive portion of the ringing signalspositive going alternations do not reach the zener potential to causethe zener diode to conduct in the reverse direction.

Diode 93 therefore rectifies incoming positive going ringing signal tofeed rectified current to capacitor 92 thereby charging it. On thenegative going incoming ringing signal diode 95 conducts chargingcapacitor 97 so that the voltage across capacitor 97 is equal to twicethe voltage appearing across capacitor 92 and may approach 200 volts DC.

Capacitor 97 continues to charge until the voltage across the capacitorsbecomes high enough to fire the neon tube 99. The firing potential ofthe neon tube 99 is preselected at a value which is less than thevoltage to which the capacitor 97 can charge. A suitable firingpotential for neon tube 99 is about 80 volts.

When the voltage across capacitor 97 rises above the firing potential ofneon tube 99, tube 99 fires to complete a discharge path for capacitor97 through resistor 98 and to thereby conduct current from the chargestored on capacitor 97. Resistor 98 limits the current that is conductedthrough the neon bulb from capacitor 97.

Upon firing, neon tube 99 will remain in conduction and will conductcurrent throughout the positive and negative alternations of the ringingsignal voltage.

The ringing signal is conventionally interrupted and thus supplied aburst by the central office equipment so that it will have the usualringing and silent intervals. In the ringing interval the 20 Hz ringingsignal will be applied to line 20 and in the silent interval it will beremoved.

The neon tube 99 will fire near the beginning of each ringing interval,remain in conduction throughout the ringing interval and will becomenon-conductive after capacitor 97 discharges at the beginning of theensuing silent interval. Neon tube 99 will therefore cycle on and off,being on or conducting in the ringing interval and being off ornon-conducting for most of the silent interval.

When neon bulb 99 conducts, it directs light onto resistor 103 to reduceresistance of resistor 103 to a negligible value and to thereby enablegate current to be fed to Triac 100 for turning the Triac on. Because ofthe cyclic operation of neon bulb 99, Triac 100 will also cyclicallyturn off and on during application of the ringing signal voltage, beingon for the ringing signals ringing interval and off for the ringingsignals silent interval. Triac 100 will turn off in the silent intervalbecause capacitor 46 blocks the flow of direct current which wouldsustain conduction of Triac 100 in absence of gate current flow.

Should Triac 100 fail to turn off because of DC being on the line, usinga zener diode 101 and capacitor 102 in parallel and inserted in serieswith the Triac 100 as shown in FIG. 2, will permit the use of the DCbiased voltage to insure that Triac 100 can be turned off.

During the ringing interval, the 20 Hz ringing signal current willtherefore be conducted through the DC blocking capacitor 46 and ringer44 in the tip party's telephone set 16 to ring the ringer. Zener diode101 is for over voltage protection of capacitor 102.

From the foregoing description it is clear ringer isolator 54 keepsringer 44 disconnected from the ground except during the time that thecentral office ringing signal voltage is applied to ring the tip party'stelephone 16. As a result, any impedance imbalance that may be caused byconnecting the telephone ringer or ringers to ground will not be presentto cause objectionable noise currents to be transmitted along with anyvoice currents when the called and calling party's are interconnected.As is well known these noise currents may develop under conditions wherethe impedance to ground on the tip side of the transmission line is notequal to the impedance to ground on the ring side of the line. Such animpedance imbalance often occurs as a result of having more ringersconnected to one side of the line than the other.

In order to ring the ring party's telephone 24 the central officeoperates to ground the tip conductor of line 20, to apply the ring tripbattery potential to the ring conductor of line 20, and to superimpose20 Hz ringing signal voltage on the negative battery potential at thering conductor of line 20. This voltage condition for ringing the ringparty's telephone 24 will not ring the tip party's telephone because noAC voltages appears across the tip party's ringer even though Triac 100is turned on.

Referring back to FIG. 1, ringer isolator 54a is the same as ringerisolator 54 as previously mentioned and makes no difference if theterminals are reversed.

In the case of ringer isolator 54a, terminal 68a is connected to tipconductor 36, and terminal 69a is connected to ring conductor 38.Additionally, ringer 44a and capacitor 46a are connected between thegrounding terminal 70a and the ring conductor 38 of drop 26 in order toprovide the potential for ringing the ring party's ringer 44a.

From the foregoing it is clear that when the central office operates toring the ring party's telephone 24, ground will be applied to terminal68a and -48 volts with the superimposed ringing signal voltage will beapplied to terminal 69a. The voltage applied to terminal 68a and 69a forringing the ring party's telephone will therefore be the same as thevoltage applied to terminals 68 and 69 for ringing the tip party'stelephone. Ringer isolator 54a will therefore operate in the same manneras ringer isolator 54 to connect ringer 44a to ground for energizing thering party's ringer. However, ringer 44a will not respond to the centraloffice voltage for ringing the tip party because no AC voltage appearson line 38 which is the ring party's line.

As compared to previously described prior art ringer isolators, it willbe appreciated that the ringer isolator of this invention has relativelyfew parts. The ringer isolator of this invention can therefore bepackaged in a small container and is economical to manufacture.

The ANI mark circuit 56 (also called the tip party's stationidentification circuit) is shown to mainly comprise a longitudinalground mark squelch circuit 150, a longitudinal control circuit 151, adifferential squelch circuit 152 and a differential switching controlcircuit 154. The circuit arrangements as described above have been namedfor convenience to relate to the type of sensing utilized by the centraloffice equipment. The longitudinal circuits will provide the ground markwith central office equipment utilizing the longitudinal method forinterrogating a ground mark on the tip party line while the differentialcircuit arrangements will be utilized by central office equipment whichdetermine the tip party utilizing differential sensing (interrogating)techniques. Briefly, the circuit arrangement of capacitor 164 and diode172 is responsive to loop current flow when the tip party's telephone 16is lifted off-hook to enable capacitor 164 to charge. When the centraloffice lifts loop current off-line 20 (i.e., interrupts loop current) tointerrogate the two-party subscriber loop circuit for the presence of aground mark (i.e., the establishment of a current path to ground),circuit 151 operates on the discharge of capacitor 164 via resistors170, 171, 157 and relay coil 155. The current discharge from capacitor164 operates (turn on) a device (in this case a transistor 165) whichcauses a ground mark to be applied to the tip party's drop 18.

The ANI equipment in the central office senses the application of theground mark (i.e., ground current path) to identify the calling party asthe tip party and to provide the operation for billing the call to thetip party in the event that the dialed call is a toll call. Since thering party has no ANI mark circuit, no ground mark will be applied tothe ring party's subscriber drop or loop circuit when the ring partycomes off-hook to initiate a call. Thus, when the central officeequipment initiates a toll ticketing condition by lifting the loopcurrent off-line 20, no ground mark will be sensed by the ANI equipmentin the case where the ring party is making the call. As a result, theANI equipment will identify the party making the call as the ring partyand will operate to bill the ring party in the event that the call is atoll call. In this manner the party dialing the toll call will beidentified for billing purposes.

Referring now in greater detail to FIG. 2, the ground mark switchingcircuit 151 which functions in cooperation with a central officeautomatic toll ticketing mechanism using a longitudinal sensing methodcomprises a ground mark resistance 166 which preferably is approximately2.2 kOhms. One end of resistor 166 is normally connected to terminal 73via a conductor 167. Terminal 73 in turn, is coupled to ground via aconductor 168 and conductor 82. Of course, if the ringer isolatorcircuitry 54 and the ANI station circuitry 56 are enclosed in a singlepackage, the interwiring may be arranged in a more convenient manner.However, the functioning of the circuit connection will be the same asshown here. The other side of resistor 166 is connected to the anodeelectrode of diode 169. The cathode electrode of diode 169 is connectedto the collector electrode of transistor 165. Transistor 165 functionsas the longitudinal ground mark switch. The emitter electrode oftransistor 165 is connected to the tip terminal 74 via a conductor 169.

Resistors 170 and 171 are connected in series with capacitor 164 betweentip in terminal 74 and tip out terminal 75. A diode 172 has its anodeelectrode connected to the emitter electrode of transistor 165 and itscathode electrode connected to the juncture of resistor 171 andcapacitor 164. Zener diode 173 has its anode electrode connected to theemitter electrode of transistor 165 and its cathode electrode connectedto the collector electrode of transistor 165 providing protection forthe emitter-collector junction of transistor 165 should an overvoltageoccur thereat. The base electrode of transistor 165 is connected to thejuncture of resistors 170 and 171.

The ground mark (the current path to ground) is provided betweenterminal 74 and ground and is therefore connected across and bridges thetip conductor to ground from the tip party's drop 32.

Under normal standby conditions with the handset 50 in its on-hookposition, switch 48 is open preventing the flow of loop current.Transistor 165 will be in its nonconducting or high impedance state,therefore the mark (current path to ground) will be open and the groundmark will be removed.

When handset 50 is removed to the off-hook position, switch 48 closesand loop current will flow because of the -48 volts appearing on thering line 34 which is connected to terminal 72. The tip line 32connected to terminal 74 is placed at ground potential by the centraloffice. Current will flow therefore from terminal 74 through diode 172to charge capacitor 164 in a relatively short period of time. Thevoltage appearing across capacitor 164 is equal to approximately thevoltage across zener diode 158 (2.7 volts). Upon interruption of theloop current by the central office, capacitor 164 will discharge viaresistors 170, 171, 157 and relay coil 155, causing a positive biasvoltage to go across resistor 170 thereby turning on (placing in aconductive state) transistor 165 thereby completing the mark currentpath from the cathode of diode 169 to the tip in terminal 74, therebyplacing the mark resistance 166 from ground to the tip side of the line.This action is sufficiently fast to place a mark interdigitally whichmay be used for Stroger Automatic Toll Ticketing (SATT) ANI systems. Bychosing the proper time constants of R and C the mark may be made toremain for as long as 300 miliseconds if required.

In order to insure that the mark circuit will permit current flow inonly one direction through transistor 165, a diode 169 is placed inseries with resistor 166 thereby further protecting transistor 165 fromdamage.

In order to prevent the mark from being placed from tip to ground duringthe ringing of the tip party by the central office coupling the ringingvoltage to terminal 72, a squelch circuit 150 has been provided whichincludes transistor 175 which has its emitter electrode connected to theemitter electrode of transistor 165 and its collector electrodeconnected to the base electrode of transistor 165. A voltage dividernetwork comprised of resistors 176 and 177 connected across terminals 72(ring in) and terminal 74 (tip in). The base electrode of transistor 175is connected to the juncture of resistors 176 and 177. Thus, when the ACringing voltage goes positive on terminal 72 with respect to terminal 74a positive bias is placed across the base-emitter electrodes oftransistor 175 thereby causing transistor 175 to conduct (turn on). Theconducting of transistor 175 causes a low resistance current flow pathbetween its collector and emitter electrodes. Since the collector andemitter electrodes of transistor 175 are connected to the base andemitter electrodes of transistor 165 respectively, when transistor 175turns on it causes a relatively low resistance path (short) between thebase emitter junction of transistor 165 thereby changing it to anonconducting state. With transistor 165 in a nonconducting (off) statethe ground mark current path through resistor 166 and diode 169 isremoved from the tip in terminal 74 as long as the voltage remainspositive.

A squelch circuit 152 which functions to remove the differential groundmark which will be described hereinafter includes a darlingtontransistor 178, which has the collector electrodes thereof connected toterminals 75 (tip out) and the emitter electrode of the outputtransistor connected to terminal 74 (tip in). A voltage divider networkwhich includes resistor 180 and 181 is connected across terminals 72(ring out) and terminal 74 (tip in). The base electrode of darlingtontransistor 178 is connected to the juncture of resistors 180 and 181.The Darlington transistor 178 is of a PNP type so that a negativevoltage appearing on terminal 72 with respect to terminal 74 will causeDarlington transistor 178 to turn-on (provide a low resistance pathbetween the output transistor collector and emitter electrodes). Thus,on the negative going half cycle of the ringing voltage the Darlingtontransistor will turn on causing the voltage from terminal 75 (tip out)to terminal 75 (tip in) to essentially reduce to zero thereby preventingthe charge to develop on capacitor 164, thus preventing the proper biasto occur and turn on transistor 165. Thus, during the ringing the groundmark path will be removed from the tip side of the line (terminal 74 toground).

It is also to be noted that when the Darlington transistor 178 is turnedon, it will prevent any voltage from appearing across capacitor 156 andthereby will prevent the differential ground mark from appearing acrossthe ring and tip lines to ground, which will be further explainedhereinafter.

In order to protect the circuitry from introducing additional noiseduring a central office battery reversal, which may occur when a call iscompleted, squelch circuit 210 is incorporated. Squelch 210 includestransistor 212 which has its collector and emitter electrodes connectedacross the base and emitter electrodes, respectively, of transistor 165.The reversal of current through resistor 157 biases transistor 212 toits on or conducting state thereby turning off transistor 165 andremoving the longitudinal mark (resistor 166) from the line.

The circuit design for voltage dividers made up of resistors 176, 177and resistors 180, 181 are made sufficiently large so that the parallelcombination thereof is greater than one meghom. The voltage dividerwhich includes resistors 180 and 181 for biasing Darlington transistor178 is designed so that it will not cause Darlington transistor 178 toturn on until a negative voltage applied across terminals 72 and 74 (thetip and ring conductors) is equal to or greater than a preselectedthreshold such as, for example -15 volts. Darlington transistor 178 willtherefore be forward biased when the central office grounds tipconductor 32 (terminal 74) and places the negative battery voltage of-48 on ring conductor 34 (terminal 72). However, Darlington transistor178 will not be forward biased and will therefore be turned off when thetip party's telephone 50 is lifted off-hook to reduce the voltage acrossthe tip and ring conductors 32 and 34 to some low value ranging fromabout -6 volts to -10 volts. Thus, during ringing both the ground marksare removed from the tip and ring lines and during dialing only thedifferential ground mark is removed.

In a typical crossbar central office switching system, the followingsequence usually takes place to establish the toll ticketing conditionafter either one of the parties comes off-hook and before dial tone issupplied to the off-hook party. First, central office equipment willmomentarily interrupt the loop current shortly after the party'stelephone is lifted off-hook; shortly after, and while the loop currentis still interrupted, the tip and ring conductors of line 20 aremomentarily shorted together and the negative battery potential of -48volts is applied by the central office to the interconnected tip andring conductors. Some central offices permit the ring conductor of line20 to float and will apply the negative battery potential to the tipconductor instead of shorting the tip and ring conductors together andapplying the negative battery voltage to both conductors. The ANI markcircuit 56 works for both types of offices.

After shorting the tip and ring conductors of line 20 together andapplying the negative battery potential to sense whether or not a groundmark has been applied, the central office crossbar system restores loopcurrent to the calling party subscriber loop and supplies the dialingtone to the calling party to permit the calling party to commencedialing. The central office senses the ground mark during the tollticketing condition and identifies the calling party as the tip party.If the central office fails to sense the ground mark, it identifies thecalling party as the ring party. After the dial pulsing is completed thecentral office transmits the identity of the calling party to theCentralized Automatic Message Accounting (CAMA) equipment to provide forthe billing of the toll call, if one was made, to the identified party.

The differential switching circuit 154 includes relay 155, capacitor156, resistor 157, zener diode 158 and diode 159 as described earlier.The winding of relay 155 is connected in series with resistor 157, whichpreferably is a small value approximately 68 ohms, and they areconnected between terminal 74 (tip in) and terminal 75 (tip out) asmentioned earlier. Relay 155 is provided with a pair of normally opencontacts 182 and 184. Contacts 182 and 184 are provided with a pair ofequally sized resistors 186 and 188 respectively, as shown, resistor 186is connected to terminal 72 (ring in) and resistor 188 is connected toterminal 74 (tip in) which places them in series across the tip and ringconductors 32 and 34 of the tip party subscriber drop 18 when the relaycontacts are closed. Contacts 182 and 184 are connected betweenresistors 186 and 188 as shown, with the earth grounded terminal 73connected to relay contact 190 which is common to both portions of thecontacts 182 and 184, thereby grounding one end of resistors 186 and 188when the relay contacts 182 and 184 are closed.

As explained earlier, during the idle condition of the line with -48volts appearing on terminal 72 Darlington transistor 178 is in the onstate causing a short across the series connection of relay coil 155 andresistor 157 therefore keeping the relay 155 in its normally openedcondition and therefore not completing the circuit from terminal 72 andterminal 74 through resistors 186 and 188, respectively, to ground.During this idle time, capacitor 156 and capacitor 164 cannot be chargedbecause no loop current is flowing in the tip party's drop 18 at thistime.

When the tip party's telephone 16 is lifted off-hook to initiate a call,loop current will flow in the direction of arrow 200. The voltage acrossthe tip and ring conductors 32 and 34 will therefore drop to a low value(e.g., 6 to 10 volts). As a result, the Darlington transistor 178 willturn off.

When Darlington transistor 178 turns off the short circuit across thewinding of relay 155 and resistor 157 will be removed. Relay 155,however, will not energize immediately because capacitor 156, being atits discharge state will create a short accross the relay winding andresistor 157.

A short time after telephone 16 is lifted off-hook, capacitor 156 willbe charged sufficiently to allow loop current to flow through thecircuit branch containing the winding of relay 155 and resistor 157 toenergize the relay. Contacts 182 and 184 will therefore close while theloop current is flowing to apply the ground mark through equalresistances (i.e., resistors 186 and 188, to the tip and ring conductors32 and 34 of the tip party's drop 18).

Capacitor 156 will be charged by the flow of loop current to the voltagethat is set by the zener potential of zener diode 158 or the voltageacross the rely coil 155. When the central office interrupts the flow ofloop current to initiate the previously described sequence to check forthe presence of a ground mark, capacitor 156 only holds relay on whilemark current flowing from the ring side of line flows through transistor165 to hold the relay on. The discharge of capacitor 164 and hence theconductivity of transistor 165 may allow the relay to drop out longbefore the end of the interrogation interval. The holding of the relayis only a by-product of the longitudinal mark resistor 166 beingconnected.

The loop current is thereafter restored by the central office, relay 155will be held in its energized state to keep the ground mark applied tothe tip party's drop 18 up to the time of dialing. When the tip party'soperating loop circuit is broken by dialing a number on telephone 16,the voltage on the tip and ring conductors 32 and 34 will be restored totheir original idle state values (zero volts on tip and -48 volts onring) for each break or open loop pulse.

As explained earlier, the Darlington transistor 178 will therefore turnon for each break portion in the dialing pulse train reapplying theshort circuit across the winding of relay 155. For each dialing pulsebreak portion therefore relay 155 will be de-energized to open contacts182 and 184 and to thereby remove the ground mark from the tip and ringconductors 32 and 34 throughout each dialing break portion. Any chargespresent on capacitor 156 at the beginning of each break portion, willdischarge through the emitter and collector electrodes of the outputDarlington transistor.

This rapid squelching operation avoids the dialing pulse distortion thatwould occur if the ground mark were not removed.

After dialing, the relay 155 will again be energized and capacitor 156will be re-charged by loop current flow. In the present embodiment,therefore, the ground mark will remain on the tip and ring conductors 32and 34 until telephone 34 is placed on-hook to open the subscriber loopcircuit and thereby interrupt loop current flow. The differential groundmark is removed as soon as the tip party's telephone 34 is placedon-hook. As described, the ANI of the present invention is capable ofoperating for both differential and longitudinal systems.

As shown in FIG. 2 the conductor 167 may be replaced by LED (lightemitting diode) 202 which is oppositely poled and connected in parallelwith diode 204. Replacing conductor 167 with the parallel combinationsof LED 202 and diode 204 permits the mark current path when applied toinclude the LED. Thus, when the mark current flows through LED 202 itwill emit rays of light indicating to an observer that the mark is onduring this period of time. Diode 204 protects the LED from reversecurrents which may damage it.

Hereinbefore has been disclosed a universal station identificationcircuit arrangement which may be utilized with central office equipmentusing either differential or longitudinal detection methods fordetecting the tip party on a two-party line. Also disclosed herein hasbeen a novel ringer isolator circuit which may be utilized with ringervoltages of much lower values than heretofore known. It will beunderstood that various changes in the details, materials, arrangementof parts and operating conditions which have been herein described andillustrated in order to explain the nature of the invention may be madeby those skilled in the art within the principles and scope of thepresent invention.

Having thus set forth the nature of the invention, what is claimedis:
 1. A universal station identification circuit arrangement for usewith central office equipment utilizing either differential orlongitudinal detection methods for identifying a preselected one of twoparties on a two-party line in a telephone system when a call isinitiated from the preselected party's telephone, comprising:(a) firstmeans for providing a first ground mark which is normally disconnectedfrom said line when sand preselected party's telephone is on-hook; (b)second means responsive to the normal flow of loop current that isestablished by lifting the preselected party's telephone off-hook forcausing said first means to apply said first ground mark to both the tipand ring conductors of said line; (c) third means for providing a secondground mark which is normally disconnected from said line when saidpreselected party's telephone is on hook; and (d) fourth meansresponsive to any momentary interruption of loop current that occursafter the flow of loop current is established by lifting the preselectedparty's telephone off hook for causing said third means to apply saidsecond mark to the tip conductor of said line.
 2. A universal stationidentification circuit arrangement according to claim 1 wherein saidfourth means applied said second mark with sufficient rapidity to becompatable with the Stroger Automatic Toll Ticketing (SATT) System forAutomatic Number Identification (ANI).
 3. A universal stationidentification circuit arrangement according to claim 1 wherein saidsecond means includes a circuit arrangement for preventing said firstmeans from applying said first mark to said tip conductor during theoccurrence of open loop dialing pulses that are transmitted from saidselected party's telephone.
 4. A universal station identificationcircuit arrangement according to claim 1 wherein said fourth meanscomprises:(a) a capacitor; (b) means for charging said capacitor withloop current flowing in the preselected party's subscriber drop when theflow of loop current is initiated by lifting the preselected party'stelephone off hook to provide a charge on said capacitor before amomentary interruption of loop current occurs; (c) current-conductingmeans; and (d) means for discharging current for said capacitor throughsaid current-conducting means when any momentary interruption occurs inthe loop current after the preselected party's telephone is off hook toinitiate a call; and (e) means under the control of saidcurrent-conducting means for coupling said second mark to at least thetip conductor of the line connecting said selected party's telephone tosaid central office whenever said capacitor discharges through saidcurrent-conducting means.
 5. The universal station identificationcircuit arrangement according to claim 4 wherein said means for chargingsaid capacitor comprises circuit means that normally provides a lowimpedance circuit path across said capacitor to discharge charge andprevent charging of said capacitor when said selected party's telephoneis on-hook to prevent the flow of loop current in the preselectedparty's subscriber drop, said circuit means being responsive to the flowof loop current that is initiated by lifting said selected party'stelephone off-hook to break said low impedance path and to thereby allowsaid capacitor to be charged by said loop current.
 6. The universalstation identification circuit according to claim 5 wherein said circuitmeans is connected across the tip and ring conductors of saidpreselected party's subscriber drop.
 7. The universal stationidentification circuit according to claim 6 wherein said circuit meansincludes:(a) a plurality of transistors; (b) a biasing circuitarrangement connected to said transistors for forward biasing saidtransistors only when the central office battery voltage across the tipand ring conductors of said preselected party's subscriber drop is abovea preselected threshold that is greater than the DC voltage that appearsacross the tip and ring conductors of said preselected party'ssubscriber drop when loop current is flowing in the preselected party'ssubscriber drop; and (c) means for connecting the emitter and collectorelectrodes of one of said transistors across said capacitor such thatwhen said transistors are forward biased, said low impedance path acrosssaid capacitor is established.
 8. A universal station identificationcircuit arrangement according to claim 4 wherein said current conductingmeans includes relay winding means and wherein said means under thecontrol of said current conducting means includes a set of contactsoperated by the flow of current through said winding means to complete acurrent conducting path between earth ground and at least the tipconductor of the preselected party's subscriber drop to establish saidsecond mark.
 9. A universal station identification circuit arrangementaccording to claim 8 wherein said winding means is connected in serieswith a diode, said diode and winding means being connected in serieswith one of the tip or ring conductors of the preselected party'ssubscriber drop, and wherein said capacitor is connected in parallelwith said diode and winding means.
 10. A universal stationidentification circuit arrangement according to claim 9 including meansfor establishing a low impedance current path across said diode and saidwinding means connected in series to prevent current from beingconducted therethrough whenever the DC across the tip and ringconductors of said preselected party's subscriber drop is at a valuethat exists when the preselected party's telephone is on hook, said lowimpedance current path establishing means being effective to open saidpath to permit current to be conducted through said control means inresponse to the reduction that takes place in the DC voltage across thetip and ring conductors of the preselected party's subscriber drop whenthe preselected party's telephone is lifted off hook to initiate theflow to loop current.
 11. A universal station identification circuitarrangement according to claim 4 wherein said current conducting meansincludes transistor means and wherein said means under the control ofsaid current conducting means includes a resistor and a diode connectedin series to complete a current conducting path between earth groundthrough the emitter and collector electrodes of said transistor meansand the tip conductor of the preselected party's subscriber drop toestablish said second ground mark.
 12. A universal stationidentification circuit arrangement according to claim 4 furtherincluding means for indicating when said current conducting meanscompletes said current conducting path between earth ground and said tipconductor of the preselected party's subscriber drop to establish saidfirst or second ground mark, said indicating means being seriallyconnected in said current conducting path.
 13. A universal stationidentification circuit arrangement according to claim 12 wherein saidindicating means includes a diode and a light emitting diode connectedin parallel and oppositely poled, said light emitting diode permittingcurrent flow therethrough and emitting light therefrom when said currentpath to establish said first or second ground mark is established.
 14. Auniversal station identification circuit arrangement according to claim4 wherein said current conducting means includes means for preventingsaid current conducting means from conducting during the application ofringing voltage.
 15. A universal station identification circuitarrangement according to claim 11 wherein said current conducting meansincludes a second transistor means connected to said transistor meansfor preventing said transistor means from conducting during theapplication of ringing voltage.